Clones of cells can be obtained from reconstructed cells which have components derived from human cell lines and strains. The ability to recombine viable cytoplasm and nuclei in the correct cell ratio and follow the behavior and growth of these cells in culture forms the basis of our proposed studies. We will study the cellular mechanisms influencing or controlling: a) the finite lifespan of the human diploid fibroblast; b) the transformed and malignant human cell. We will attempt to alter the lifespan of a cell by the addition of malignant or transformed cell components, and monitor the protein synthesis of the nucleus by studying the Hl-A surface determinants on the membrane of the reconstructed cell. By studying the effects of varied cytoplasmic environments on the aged and malignant nucleus through the technique of cell reconstruction and nuclear transfer, the regulation of function and gene action can be evaluated. The modulation of cellular growth characteristics, possibly senescence and malignancy may thus be feasible.